Various vibration wave driven apparatuses that drive a driving member by causing a certain mass point to perform elliptic motion have been proposed. Japanese Patent Laid-Open No. 2004-320846 describes a basic structure of a vibration wave driven apparatus. FIGS. 12A and 12B show an exterior perspective view illustrating the structure of the vibration wave driven apparatus described in Japanese Patent Laid-Open No. 2004-320846. As show in FIG. 12A, the vibration wave driven apparatus includes a vibration member including a rectangular plate-shaped elastic member 4 made of a metal material. A piezoelectric element 5, which is an electro-mechanical energy conversion element, is bonded to a back surface of the elastic member 4. A plurality of projection portions 6 are provided on a top surface of the elastic member 4 at predetermined positions.
In this structure, an alternating voltage is applied to the piezoelectric element 5, so that bending vibration of the elastic member 4 in a second vibration mode along the long-side direction thereof and bending vibration of the elastic member 4 in a first vibration mode along the short-side direction thereof are simultaneously generated. As a result, elliptic motion is excited in the projection portions 6. A driving member 7 is brought into pressure contact with the projection portions 6 so that the driving member 7 can be linearly moved by the elliptic motion of the projection portions 6. In other words, the projection portions 6 function as a driving portion of the vibration member.
As shown in FIG. 12B, the piezoelectric element 5 is polarized, and includes two electrodes A1 and A2. When alternating voltages V1 and V2 in the same phase are applied to the two electrodes A1 and A2, respectively, bending vibration in the first vibration mode having two nodes that extend in a direction parallel to the long-side direction of the elastic member 4 is excited. This is the first mode vibration. When alternating voltages V1 and V2 in the opposite phases are applied to the two electrodes A1 and A2, respectively, bending vibration in the second vibration mode having three nodes that extend in a direction parallel to the short-side direction of the elastic member 4 is excited. This is the second mode vibration. The combination of the first mode vibration and the second mode vibration generates the elliptic motion of the projection portions 6. When the driving member 7 is brought into contact with the projection portions 6 in this state, the driving member 7 can be linearly moved.
According to the vibration wave driven apparatus described in Japanese Patent Laid-Open No. 2004-320846, velocity control can be performed by changing the frequency or the phases of the two alternating voltages that are applied to the piezoelectric element.